The present invention relates to a transmission apparatus for connecting a plurality of LANs (Local Area Network) to each other and constructing a fast and high-capacity back bone network, a network transmission system for constructing a plurality of routes by connecting a plurality units of the transmission apparatus to each other, and to a transmission method for realizing a relay as a backbone with those transmission apparatus.
FIG. 30 is a block diagram showing a network transmission system in a building for an ordinary business organization. Constructed in the building shown in FIG. 30 is a LAN using floors from a first basement to a third floor. Routers RT1, RT2, and RT3 are installed in the third floor, second floor, and first floor respectively, and those routers RT1, RT2, and RT3 are connected to a transmission apparatus 100 as a backbone for the routers installed in the first basement.
As for a system in each floor, a plurality of hubs HB1 . . . HBi (i: a natural number) are connected to the router RT1. A plurality of hubs, not shown through, are connected to each of the other routers RT2, and RT3 similarly to the router RT1. Terminals TL1 . . . TLj (j: a natural number) for a server or a work station or the like are connected together onto the hub HB1, and terminals PC1 . . . PCk (k=a natural number) connected together onto the hub HB2. It should be noted that the same system as the relation among the router, the hubs, and the terminals shown in the third floor is installed also in the first floor and the second floor.
The transmission apparatus 100 has also a plurality of hubs and terminals connected thereto under controls by its own like the routers RT1, RT2, and RT3 on each floor and also connects other transmission apparatus thereto.
Description is made for a case, as an example of operations in the network transmission system shown in FIG. 30, where the terminal TL1 in the third floor transmits data to any terminal in the second floor. A protocol to be used is a TCP (Transmission Control protocol)/IP (Internet Protocol) protocol as one example.
FIG. 31 is a view schematically showing a format of a frame (also called as a packet) used in the TCP/IP protocol. The frame comprises, as shown in FIG. 31, from the header to the end thereof, a start flag indicating a start of the frame, a MAC (Media Access Control) header for defining a destination MAC address and a source MAC address or the like, a type value for defining a protocol type, an IP header for defining a destination IP address and a source IP address or the like, a frame check sequence (FCS) for data and a checksum, and an end flag indicating an end of the frame.
Herein a MAC address and an IP address of a source terminal TL1 are MACA and IPA, and a MAC address and an IP address of a destination terminal are MACB and IPB, respectively. Further MAC addresses of the router RT1, the transmission apparatus 100 and the router RT2 provided for relaying data between the terminal TL1 and a destination terminal are MACC, MACD, and MACE respectively.
At first, the terminal TL1 prepares a frame according to the format shown in FIG. 31. Defined in the MAC header of the frame, during the preparation, is a MAC address (MACC) of the router RT1 through which the frame passes first of all when transferred to the destination terminal as a destination MAC address together with the MAC address (MACA) of the source terminal. Defined also in the IP header thereof is an IP address (IPB) of a destination terminal together with the IP address (IPA) of the source terminal.
When the frame is sent out onto a network by the terminal TL1, the frame is first received by the router RT1. This router RT1 extracts the IP header as well as the MAC header from the received frame. Further the router RT1 confirms from the IP header that the source terminal is the terminal TL1 (IPA) and the destination is a terminal having an IP address of IPB, and then rewrites the MAC header to MACD for the transmission apparatus 100 as the following MAC address. As described above, the router RT1 transmits the frame with the updated MAC header to the transmission apparatus 100 as a backbone.
The rewriting operation of the MAC header is also executed in the following transmission apparatus 100 and the router RT2. Namely, the MAC address is rewritten from MACD to MACE in the transmission apparatus 100, and the MAC address is rewritten from MACE to MACB in the router RT2. As described above, the MAC header is updated each time data passes through the router in data transmission through the router.
A large amount of traffic generated in each floor is concentrated to the transmission apparatus 100 in this network transmission system, which makes it necessary to select a transmission apparatus having a large capacity and high-speed capability.
There is, as a transmission apparatus with a large capacity capable of connecting a plurality of routers to each other, a combination of a switching hub with a router and a combination of an ATM (Asynchronous Transfer Mode) switch with a router other than the transmission apparatus 100 (router). FIG. 32 is a block diagram schematically showing a transmission apparatus constructed by a combination of a switching hub with a router, and FIG. 33 is a block diagram schematically showing a transmission apparatus constructed by a combination of an ATM switch with a router.
A transmission apparatus 200 shown in FIG. 32 has a router 201 and a switching hub 202 connected to each other. The switching hub 202 executes bridging among transfer paths a, b, c as well as among transfer paths d, e, f, and also performs switching between the transfer paths a, b, c and the transfer paths d, e, f. This switching hub 202 relays, if applied in an OSI (Open Systems Interconnection) layer, a layer corresponding to the layer 2 thereof. Namely, the switching hub 202 transparently relays, by selecting a route according to the MAC address, the frame flowing on the LAN.
Also, the router 201 receives the frame from the switching hub 202, rewrites data such as the MAC address, TTL (Time to Live), and a checksum to new ones, and returns the frame to the switching hub 202 (e.g., rewriting the MAC address from MACX to MACY). This router 201 relays, if applied an OSI layer, a layer corresponding to the layer 3 thereof. The router 201 receives, by selecting a route according to the IP address, the frame running on the LAN, rewrites the frame to new one, and then relays the rewritten frame to other LAN.
A transmission apparatus 300 shown in FIG. 33 has a server 302 and routers 303, 305 connected to an ATM switch 301. In FIG. 33, the router 303 positioned in the input side of the ATM switch 301 divides the frame into data units each called as a cell having a short fixed length by an ATM board 304 incorporated therein and transmits the units to the ATM switch 301. On the other hand, the router 305 positioned in the output side of the ATM switch 301 returns each cell to the frame by an ATM board 306 incorporated therein and then transmits the frame.
The ATM switch 301 relays, if applied in the OSI layer, layer corresponding to the layer 1 thereof according to the cells running between the routers 303 and 305. This ATM switch 301 selects a destination router (route) with a support by the server 302 in which the destination information is stored. Namely, a route is selected by an identifier unitrarily allocated thereto and specific to the ATM in the ATM switch 301. In this example, the destination router is the router 305.
In the transmission apparatus 200 shown in FIG. 32, however, the frame is rewritten at the router 201 when passing therethrough even if the switching hub 202 can transparently pass the frame therethrough. For this reason, it is satisfactory in the functional aspect that the layer as far as the layer 3 can be covered, but reduction of a processing speed as a whole can not be avoid.
Accordingly, the transmission apparatus 200 has only low performance as a backbone transmission apparatus that requires high-speed capability. To avoid this problem, a large increase in cost is forced, which makes it difficult to be realized.
Also, in the transmission apparatus 300 shown in FIG. 33, the router 303 and 305 or the like connected to the ATM switch 301 execute conversion processing between a frame and cells even transparency is obtained in the area of ATM switch 301, so that an increase in cost per interface can not be prevented. For this reason, the transmission apparatus 300 has only a system obtained by distributing a load onto periphery of the ATM switch 301 so that the load on the ATM switch 301 itself is reduced, and for this reason the system as a whole is comparatively costly.
In order to solve the problems described above, it is necessary to construct a network transmission system which has both functions of the transmission apparatus 200 and 300, namely which can be completely transparent to a frame passing therethrough with low cost and high speed.
Consideration is made for the network transmission system for realizing this transmission completely transparent to a frame. FIG. 34 shows a network transmission system for coupling a plurality of transmission apparatus each of which is completely transparent to a frame passing therethrough to each other with a tree structure or a loop structure (a triangle structure as an example) and generating a plurality of routes when a relay is performed with this plurality of transmission apparatus.
In FIG. 34, each of transmission apparatus 401, 402, and 403 which can be completely transparent to a frame is connected to the other two transmission apparatuses. The transmission apparatus 401 is connected to a subnet SNC via a router RTC1, and the transmission apparatus 402 is connected to the subnet SNC via a router RTC2. Further connected to the subnet SNC is, for example, a terminal TLC. Also, the relay 403 is connected to a subnet SNB via the router RT1. Further connected to the subnet SNB is, for example, the terminal TL1.
When a frame is transmitted from the terminal TL1 of the subnet SNB to the terminal TLC of the subnet SNC in the network transmission system shown in FIG. 34, there are two types of route such as a route A and a route B. In the route A, a frame sent out from the terminal TL1 arrives the terminal TLC through the router RT1, transmission apparatus 403, transmission apparatus 401, and router RTC1. In the route B, on the other hand, a frame sent out from the terminal TL1 arrives the terminal TLC through the router RT1, transmission apparatus 403, transmission apparatus 402, and router RTC2.
In the route A, as described above, the transmission frame to pass through the transmission apparatus 403 and 401 is completely and transparently passed therethrough without being rewritten. For this reason, the frame transmission can maintain its high-speed capability even when having passed through the transmission apparatus 403 and 401. Similarly, in the route B, the transmission frame to pass through the transmission apparatus 403 and 402 is completely and transparently passed therethrough without being rewritten. For this reason, the frame transmission can maintain its high-speed capability even when having passed through the transmission apparatus 403 and 402.
However, in the network transmission system for realizing transmission completely transparent to a frame passing therethrough as shown in FIG. 34, under the condition of forming a multipath at the same cost, namely, under the condition where each of the route A and the route B from the terminal TL1 to TLC passes through a router only once, so that cost of the communication for each route is the same, but in the state where two routes A and B exist, a router as a next hop in peripheral routers in each routes is different according to an arriving order of frames each for a routing protocol, table preparation with the frames each for a routing protocol, and to a difference in versions of updated control programs.
Namely, in those cases, the contents of an external routing table held by the transmission apparatus 403 for relaying the two routes A, and B as a multipath each at the same cost is differentiated from the contents held by peripheral routers of the router RT1, which may cause communications through the transmission apparatus 403 to be incorrectly executed.
For example, if the route A is selected in the transmission apparatus 403 and the route B is selected by the router RT1, the router RT1 sends the frame to the router RTC2, but the transmission apparatus 403 sends the frame to the router RTC1, and the frame can not be received by the router RTC1. Namely, as the router RT1 adds a destination MAC address for the router RTC2 to the frame, the router RTC1 abandons the frame because the destination MAC address is recognized as not for the router.
It is a first object of the present invention to obtain, for the purpose of solving the problems based on the conventional technology, a transmission apparatus enabling realization of high-reliability communications by maintaining the compatibility with each routing even under the condition of forming a multipath at the same cost for realizing cost performance of the apparatus as a whole without being restricted to the transmission method applied to the OSI layers based on the conventional technology.
It is a second object of the present invention to obtain, for the purpose of solving the problems based on the conventional technology, a network transmission system enabling constriction of a high-reliability system by applying there in the transmission apparatus which can achieve the first object.
It is a third object of the present invention to obtain, for the purpose of solving the problems based on the conventional technology, a transmission method, in which relaying as a backbone can be performed so as to enable realization of cost performance of the apparatus as a whole without being restricted to the transmission method applied to the OSI layers based on the conventional technology, enabling realization of high-reliability communications by maintaining the compatibility with each routing even under the condition of forming a multipath at the same cost.
With the transmission apparatus according to the present invention, a plurality of routes are previously formed in the network transmission system, and if there exists information concerning a plurality of routes each constituting a multipath each at the same cost of the route information including cost information stored in correlation to the destination information, by using information for any one of the plurality of routes, the route is fixedly used for relaying, so that a unique route is notified to networks connected to each other through the transmission apparatus so that information for only one route can be identifiable, and with this feature, it is possible to realize high-reliability communications by maintaining the compatibility with each routing even under the condition of forming a multipath at the same cost for realizing cost performance of the apparatus as a whole without being caught by the transmission method applied to the OSI layers based on the conventional technology.
With the transmission apparatus according to the present invention, a plurality of routes are previously formed in the network transmission system, and when information concerning a plurality of routes each constituting a multipath each at the same cost is constructed by received control information, information for a route to be used for relaying is constructed according to information for any one of the plurality of routes, so that a unique route can be given to the system even if a plurality of routes constituting a multipath each at the same cost exist, and with this feature, it is possible to realize high-reliability communications by maintaining the compatibility with each routing even under the condition of forming a multipath at the same cost for realizing cost performance of the apparatus as a whole without being caught by the transmission method applied to the OSI layers based on the conventional technology.
With the transmission apparatus according to the present invention, a plurality of routes are previously formed in the network transmission system, and when information concerning a plurality of routes constituting a multipath each at the same cost is constructed by a received routing protocol, information for a route to be used for relaying is constructed according to information for any one of the plurality of routes, so that a unique route can be given to the system even if a plurality of routes constituting a multipath each at the same cost exist, and with this feature, it is possible to realize high-reliability communications by maintaining the compatibility with each routing even under the condition of forming a multipath at the same cost for realizing cost performance of the apparatus as a whole without being caught by the transmission method applied to the OSI layers based on the conventional technology.
With the transmission apparatus according to the present invention, of information concerning a plurality of routes constituting a multipath each at the same cost, a routing table is constructed according to route information for giving permission of a relay, and also constructs a non-routing table according to route information for not giving permission of a relay. With this feature, of the information concerning a plurality of routes constituting a multipath each at the same cost, a frame can be transmitted only through a unique route according to the routing table, and route information for the other routes is deleted according to the non-routing table, so that it is possible to coincide contents of a routing table in a peripheral router with contents of a routing table in a transmission apparatus.
With the transmission apparatus according to the present invention, when the route information included in the received frame is included in the non-routing table, the route information is deleted and the frame without the route information is transmitted, so that the information concerning a plurality of routes constituting a multipath each at the same cost having existed at the time of reception thereof disappears at the stage of frame transmission, and a unique route on the system can be notified to the network.
With the network transmission system according to the present invention, a plurality of routes are previously formed with a tree structure or a loop structure comprising a plurality of replay apparatuses in the network transmission system, and when information concerning a plurality of routes constituting a multipath each at the same cost exists among the route information including cost information stored in correlation to the destination information in each of the transmission apparatus, the frame is fixedly relayed by using information for any one of the plurality of routes, so that a unique route is notified to networks connected to each other through the transmission apparatus so that only one route information can be identifiable, and with this feature, it is possible to construct a high-reliability system by maintaining the compatibility with each routing even under the condition of forming a multipath at the same cost for realizing cost performance of the system as a whole without being caught by the transmission method applied to the OSI layers based on the conventional technology.
With the network transmission system according to the present invention, a plurality of routes are previously formed with a tree structure or a loop structure comprising a plurality of replay apparatuses in the network transmission system, and when information concerning a plurality of routes constituting a multipath each at the same cost is constructed by the received control information in each of the transmission apparatus, information for a route to be used for relaying is constructed according to information for any one of the plurality of routes, so that a unique route can be given to the system even if a plurality of routes constituting a multipath each at the same cost exist, and with this feature, it is possible to construct a high-reliability system by maintaining the compatibility with each routing even under the condition of forming a multipath at the same cost for realizing cost performance of the system as a whole without being caught by the transmission method applied to the OSI layers based on the conventional technology.
With the network transmission system according to the present invention, a plurality of routes are previously formed with a tree structure or a loop structure comprising a plurality of replay apparatuses in the network transmission system, and when information concerning a plurality of routes constituting a multipath each at the same cost is constructed by the received routing protocol in each of the transmission apparatus, information for a route to be used for relaying is constructed according to information for anyone of the plurality of routes, so that a unique route can be given to the system even if a plurality of routes constituting a multipath each at the same cost exist, and with this feature, it is possible to construct a high-reliability system by maintaining the compatibility with each routing even under the condition of forming a multipath at the same cost for realizing cost performance of the system as a whole without being caught by the transmission method applied to the OSI layers based on the conventional technology.
With the transmission method according to the present invention, there are steps of executing, when having received the frame related to the multipath at the same cost from each of the networks, deletion of any of entries in the received frame or transmission of the frame following the entry (entries) according to whether destination information as well as the cost for each of the entries are identified to those in the routing table or not, so that frame transmission through a multipath at the same cost can be controlled for each route according to the destination, and with this feature, it is possible to realize high-reliability communications by maintaining the compatibility with each routing even under the condition of forming a multipath at the same cost.